Isolation of styrene by azeotropic distillation with ethylene diamine



March 29, 1949.

Filed Jan. 22, 1946 FIRST cur non-swa Non-swam: mono- HYDROCARBONSAND WATER CARBONS REMOVED 2ND CUT an N RE a OONCENTRATE counmme CONDENSER AGENT STYRENE CONCENTRATE CONTAINING AGENT REMOVED f WATER INlTIALLY RETURNED LATER REMOVED WATER FR'ACTIONATING COLUMN STYRENE counmme ETHYLENE DIAMINE PHENYLACETYLENE AZEOTROPIC AGENT V r INVENTOR PHENYLACETYLENE r Karl 49? Patented Mar. 29, 1949 ISOLATION OF STYRENE BY AZEOTROPIC DISTILLATION WITH ETHYLENE DIAMINE Karl H. Engel, Teaneck, N. 1., assignor to Allied Chemical .& Dye Corporation, New York, N. Y., a corporation of New York Application January 22, 1946, Serial No. 642,754

18 Claims.

This invention relates to the production of substantially pure styrene or a hydrocarbon oil of high styrene content from hydrocarbon oils of relatively low styrene content. I

Styrene is found in low concentration in hydrocarbon oils, particularly aromatic hydrocarbon oils, produced in such operations as coal distillation, gas production, and petroleum cracking and reform ng. An aromatic hydrocarbon oil containing varying proportions of styrene in admixture with other aromatic hydrocarbons is also obtained when styrene is producedsynthetically, e. g., by cracking or dehydrogenation of alkyl benzenes. From these hydrocarbon oils. styrene cuts may be obtained by fractional distillation, which cuts may contain as much as about 50% styrene, the remainder consisting chiefly of like,- boiling aromatic hydrocarbons such as the xylenes and ethylbenzene,- and sometimes also minor amounts of aliphatic and naphthenic hydrocarbons bollingclose to styrene; the styrene .oils thus produced generally contain phenylacetylene admixed therewith. Phenylacetylene, as is well known, interferes with proper polymerization of styrene and is, accordingly, undesirable in styrene that ,is to be used for the production of polymerized products, e. g. resins. As above indicated, styrene cannot be readily separated from the close-boiling hydrocarbons, including phenylacetylene, with which it is generally associated lay-ordinary fractional distilla: tion. Although some concentration of phenylacetylene in the overhead product is eifected, suilicient is left in the styrene bottoms to give poor polymerization qualities to the styrene; moreover, the yield-of monomeric styrene from such separation is poor. It has been. proposed heretofore to recover substantially pure styrene by bringing about polymerization of the styrene in'the styrene oil, separating the non-styrenecomponents from the polymerized styrene by distillation, and then cracking the polystyrene by application of heat, whereupon a substantial part of the polystyrene depolymerizes to form monomeric styrene. As this process has generally been carried out in the published prior art, the yield of monomeric styrene has been low, and a styrene product is produced in whichthe styrene is still admixed with close boiling hydrocarbons.

It has also been proposed to remove phenylacetylene from a styrene oil by chemical means, for example, by treatment with an ammoniacal cuprous or silver salt. Such methods are disadvantageous for economic reasons, both because of the cost of the reagents used and the cost of the handling 2 v oi the styrene oil needed to accomplish removal of the acetylenic constituents.

It is an object of this invention to provide a distillation process for separating styrene in good yield from the oils in which it occurs.

It is a further object of this invention to provide a process in which substantially pure styrene may be obtained in a single distillation operation from the usual styrene fractions which may contain, for example, about 50 wt. percent styrene, obtained by fractional d'stillation of styrene-containing oils produced in coke-oven operations, water-gas and oil-gas production, the cracking and reforming of petroleum oils, and styrene synthesis.

It is another object of the invention to provide a process for the recovery of styrene from aromatic oils containing styrene and close-boiling benzene homologs such or ortho-xylene, meta-xylene and para-xylene.

It is a further object of this invention to provide a process in which substantially pure styrene, free from phenylacetylene, may be obtained by distillation from theusual crude styrene fractions which contain styrene in admixture with other hydrocarbons, including phenylacetylene.

I have discovered that substantially pure styrene or a hydrocarbon oil greatly enriched in styrene may be separated from a styrene oil containing styrene, along with hydrocarbons-including aromatic hydrocarbons, not readily separable from styrene, by ordinary fractional distillation, by carrying out fractional distillation of a mixture of such styrene oil and ethylene diamine. The styrene oil fractions subjected to azeotropic. distillation may have a boiling range of from to C. at a pressure of 760 mm. of mercury.

The ethylenediamine, I have found, on addition to a styrene oil, as above described, containing other hydrocarbons besides styrene, form azeotropes of a minimum boiling type with the various hydrocarbon constituents of the oil; i. e., when a: mixture of the hydrocarbon oil and ethylene diamine is distilled, various hydrocarbon-agent mixtures distill over at temperatures lower than the distillation temperatures of the hydrocarbon and of the azeotropic agent forming such mixtures.

Moreover, I have made the surprising discoverythat the azeotropic mixture thus formed between the agent as above described, and the non-styrene hydrocarbons, other than phenylacetylene 'con--' tained in the styrene oil, have substantially lower distillation temperatures than the aze'otropio above indicated,

. aliphatic substituents includ materials, upon first as azeotropic mixtures with the azeotropic agent, and material whose hydrocarbon component consists of substantially pure styrene or highly enriched styrene may be left as still residue when treating an oil substantially free of phenylacetylene.

Thus, when distilling a hydrocarbon oil free of phenylacetylene, in accordance with my invention, an oil consisting of substantially pure styrene may be obtained as the desired product.

' When a hydrocarbon oil containing phenylacet-' ylene is distilled in accordance with my invention, I have found the non-styrene hydrocarbons, other than phenylacetylene, are distilled on first as azeotropic mixtures with the azeotropic agent hereinabove described, and thereafter the styrene comes of! as an Meotropic mixture with the agent, and finally the phenylacetylene. Notwithstanding the fact that phenylacetylene has a lower boiling point than styrene, the azeotropic mixture formed by the agent and styrene, hereinabove described, has a substantially lower distillation temperature than the azeotropic mixture of the agent and phenylacetylene: this difference is sufficiently great so that upon fractional distillation of the agent and styrene oil mixture, substantially all of the styrene is distilled oi as an azeotropic mixture with the agent before any-phenylacetylene comesoff. A material whose hydrocarbon component consists of phenylacetylene may then be distilled off as a higher fraction or may be left as still residue.

Hence, in accordance with my invention, when treating hydrocarbon oils containing phenylacetylene, the oil may be distilled in the presence of the agent, so that in one operation, by careful fractional distillation, there is obtained a styrene fraction which is substantially pure, leaving a still residue of hydrocarbon 011 containing phenylacetylene. Alternatively, distillation may be carried out in two operations, the flrstof which resulting in the oil containing I tially separation of the non-styrene phenylacetylene, and the thus parpurifled styrene containing phenylacetylene re-distilled in the presence of the azeotropic agent; hereinabove described, to separate the styrene from the phenylacetylene.

Examples of styrene-containing oils which, as may be obtained by fractional distillation of the light aromatic hydrocarbon oils recovered in gas production, coke oven operation, petroleum cracking and reforming, styrene synor similar operations involving synthesis or pyrolysis of aromatic hydrocarbons containing oil which settles out from carburetted water-gas or oil-gas mains; (2) the light oils recovered by scrubbing of coke oven gas, carburetted watergas and oil-gas; (3) the lower boiling fractions distilled from coal tar, and oil-gas tar; (4) cracked and reformed petrolemn oils; (5) the products of styrene synthesis involving, alkyl benzenes; and (6) the products of similar processes involving the synthesis or pyrolysis of aromatic hydrocarbons containing aliphatic substituents, e. g. the product of pyrolysis of a polystyrene resin, From such styrene-containing fractional distillation, close-cut fractions boiling, for example, through the range carburetted water-gas tar" of Mir-146' C., at 760 mm. of mercury pressure, may generally be obtained.

From the first four sources named above, for example, styrene fractions containing up to about .5096 styrene by weight are generally obtained;

from the other two sources, styrene fractions of higher styrene content may be obtained upon fractional distillation of the original styrene-containing material. Such fractions generally con tain v rying proportions of styrene, phenylacetylene usually in amount exceeding .05% by weight. substantial proportions of other aromatic hydrocarbons having boiling points close to that of styrene, for example, xylenes, ethylbenzene and other alkyl benzenes, and aliphatic (including naphthenic) hydrocarbons boiling in the neighborhood of the boiling point of styrene.

The term like boiling compounds, with reference to styrene, as used herein, refers to those non-styrene hydrocarbons such as xylenes and ethylbenzena, generally associated with styrene in styrene fractions and to other compounds present in styrene oils which, upon fractional distillation of the oils, tend to distill with the styrene. Styrene fractions produced as above described are, in general, suitable for distillation with the azeotropic agent hereinabove set forth, in accordance with my invention, to produce substantially pure styrene or a; hydrocarbon oil 80 greatly enriched in styrene.

It ts generally advantageous to subject the styrene crude which is to be azeotropically distilled to preliminary purification. For example,

: (l) drip oil, they for example, the pyrolysis of "an-auxiliary such purification may. 'of styrene oils recovered particularly in the case from drip oils, light oils,

and tar distillates, consist of washing with sulfuric acid followed by neutralization and distil lation. vOther methods of purifying styrene oils are known in the art. Such purification may be carried out either prior to or following the above described fractionation to produce a close-cut styrene fraction.

The fractional distillation of azeotropic mixtures of a styrene hydrocarbon oil which may or may not contain phenylacetylene and an azeotropic agent as described above, may be carried out as a simple batch or continuous distillation in which the entire amount of agent needed may be added to the styrene oil before fractionation. Alternatively, the agent may be added gradually in continuous or intermittent fashion during the course of the fractionation. Inthe latter case, the agent recovered from the distillation during fractionation, as described below, may be returned to the still and an amount of agent may thus be employed in the process substantially less than the total amount supplied to the still during distillation. One method of bringing about continuous recovery of agent from the distillate during fractionation and its return to the still is to have water present in the upper part of the fractionation column, as morefully described below. The water may be looked upon as azeotrcpic agent in this case.

If ethylene diamine agent isadded to the styrene oil to be subjected to azeotropic fractionation in a single additio the amount'should be regulated sothatthere will not be an undue excess remaining in the still residue when fractional distillation is discontinued. If no phenylacetylene is present in the oil, the azeotropic distillation of styrene may be unnecessary. In that case there should be at least sumcient agent used to remove substantially all non-styrene hydrocarbons in the azeotropic' distillates. If it is deagent is added intermittently, or if it is cyclieally returned to the still, enough agent should be present at all times. for most efilcient operation, to form azeotropes with all hydrocarbons held in the fractionating column during operation or in the portion of the column (if water is used as auxiliary agent) in which separation of hydrocarbons from each other is effected.

The azeotropic distillation of the styrene oil which may or may not contain phenylacetylene with the agent, with or without water as an auxiliary agent, may be carried out either batchwise oi continuously. In a batchwise fractionation not employing water as auxiliary agent, anhydrous ethylene diamine is preferably used: the distillate at first consists almost entirely of the azeotropic mixture of the agent and non-styrene oil other than phenylacetylene, but as fractionation-proceeds and the temperatureapproaches the dis-' tillation temperature of the agent-st rene azeotrope, the styrene content of the distillate gradually increases. However, auueous mixtures of the'agent, which may be available, may be used. when using such aqueous mixtures, for most efllcient operation of the fractionating column. the water obtained in the first distillation should be removed from the system until substantially anhydrous agent remains The course of the fractionation may be followed by taking samples of the distillate and testing them for their styrene content. When the distillate te ts svfll iently hi h in st rene, the styrene product may then either be withdrawn from the still or taken as a final distillate fraction.-

If phenylacetylene is present, the initial fractions are the same as above set forth, and as the fractionation continues to the point where the greater part of the styrene has been distilled over and the temperature of the still approaches the distillation temperature of the a ent-phenvb.

acetylene azeotrope, a small proportion of the phenylacetylene may be in to come over with the styrene. The distillation may be stopped at this point. leaving as s ill res due. residual styrene containing phenylacetylene which may. be subjected to a separate azeotro ic distillation to effect separation of residual styrene from the phenylacetylene.

The course of the fractionation may be followed by taking samples of the distillate and testing them for phenylacetylene. This is done by shaking a small sample with an equal volume of 5% ammoniacal silver nitrate solution and noting the precipitate formed. The distillation is advantageously continued until the phenylacetylene content of the distillate rises to not more than about 0.03% by weight to obtain maximum re-- covery of styrene and still not have present an objectionable amount of phenylacetylene, such, for example, as would interfere with the subsequent polymerization of the styrene. Preferably.

a styrene fraction is isolated, containing substantially less than .03% phenylacetylene,

In continuous operation, the styrene oil and azeotropic agent may be continuously introduced into an intermediate portion of the fractionating column. A product whose oil component is subtantially pure styrene, when distilling an oil substantially free of phenylacetylene, or a greatly enriched styrene oil, may be continuously within the column and still hydrocarbon,

drawn from the still and an azeotropic mixture of non-styrene hydrocarbon and agent may be continuously taken of! overhead; This distillate may be condensed, the agent separated as described below, and theseparated agent returned to the fractionating column along with the entering styrene oil.

When distilling an oil containing phenylacetylene, after separation of hydrocarbons other than phenylacetylene, boiling close to styrene from this oil, a product whose oil component is substantially pure styrene may be continuously taken of! overhead-in the form of an azeotropic mixture'with the agent, and a phenvlacetylene concentrate may be continuously withdrawn from the still. The pure styrene containing distillate may be condensed, the agent separated as described below, and the separated agent returned to the fractionating column along with the entering styrene oil. i

In batchwise distillation employing water as auxiliary agent, a charge of styrene oil which may or may not contain phenylacetylene, primary agent, namely, ethylene diamine and water is placed in the still and subjected to fractional distillation. Instead of placing the water in the still, it may be added directly to the top of the column. The water forms azeotropes of the socalled eutectic type with the hydrocarbon oils carried upward in the column in azeotrooic mixtures with the primary agent. Inasmuch as the water-hydrocarbon azeotropes have lower boiling points than the corresponding primary agenthydrocarbon azeotropes, the primary agent, in general, is substantially replaced by water. Applied in limited proportions, the water is completely volatilized from the still charge and is eventually found in substantial proportions only in the upper part of the fractionating column and in the distillate. As the distillate is condensed, it stratifies into a water layer and a hydrocarbon layer, generally substantially free from primary agent. The water layer may be continuously returned to the top of the column. In the upper part of the column, therefore, water in the liquid state, along with some condensed flows downwardly countercurrent to vapors of water, hydrocarbon and agent passing upwardly through the column; after o eration has commenced with addition of a limited amount of water to the still, the water is driven up into the column, leaving anhydrous agent in the still charge.

This water flowing downwardly through the upper part of the column, eventually is a ain vaporized, its vapors displacing selectively the primary agent vapors in azeotro ic mixtures with hydrocarbons in the upper portion of the column, the displaced primary agent vapors in turn being condensed and flowing downward in countercurrent .to rising fresh hydrocarbon vapors. Thus, water, as well as the primary agent, are completely retained in the still system, and are largely retained in the fractionating column. The quantity of water is determinedby the size of the column. the column hold-up and by the proportion of the column which is intended to be operated with the water-az'eotrope present therein. By selecting the proper proportion of water to column capacity, water in liquid or'vapor phase is confined to generally one-fifth of the column space at the top, the lower four-fifths holding the primary agent as liquid or vapor, a larger column space being required for the more dimcult separation of styrene'i'rom other hydrocarbons. As

2,400,115", J g j/ in the batchwise distillation above described, distillation is continued until a styrene product of desired purity is obtained, either as still residue or final distillate fraction.

The distillation employing water as auxiliary azetropic agent may also be carried out continuously by continuously introducing a mixture of the styrene oil, which may or may not contain phenylacetylene, and primary azeotropic agent into an intermediate portion of the fractionating column of a still and column system wherein a hydrochloric acid and the aqueous liquid decanted and treated with an aqueous alkali solution. e. g. an alkali hydroxide or alkali carbonate solution, to spring the organic base, which forms a separate liquid layer.

Alternatively, the agent may advantageously be recovered from the hydrocarbon oils in which mixture of the styrene oil and primary agent is being fractionated; water for the fractionation is introduced continuously or intermittently, preferably, into the top of the column. As in the batchwise procedure above described, all or the greater part of the water needed for fractionation may be provided by continuous return of the water component of the condensed distillate to the top of the fractionating column.

When distilling an oil containing phenylacetylene, the distillation may be carried out as above described, taking oil as distillate first the nonstyrene hydrocarbons other than phenylacetylene as an azeotropic mixture with the agent and water, and then substantially all of the styrene as an azeotropic mixture with the agent, leaving as still residue an oil containing substantially all of the phenylacetylene or a mixture of the phenylacetylene and a portion of the'styrene may be left as still residue, which is later subjected to a separate azeotropic distillation, as hereinabove de-.

' scribed, to separate the styrene from the phenylacetylene.

The degree of fractionation, determined by the number of plates employed in the fractionating column, the point at which batchwisefractionation is discontinued. and the styrene content of the hydrocarbon oil being treated, is controlled so as to give a final product of particular styrene content. subjecting a closecut styrene fraction to azeotropic distillation, as herein described, to continue fractionation until the distillate comingover or the material remaining in the still has at least a 95 %.styrene content (by weight), based on the oil component of the material. By more I have found it advantageous when exhaustive azeotropic fractionation or refrac.

tionation of a styrene-enriched oil, styrene concentrations of 98% to 100% may be obtained.

I have found it advantageous to carry out the distillation at still temperatures not exceeding about 65 C., with correspondingly low vapor pressures not above about 30 mm. of mercury in the system, if no polymerization inhibitor is used. If effective inhibitors are used, such as hydroquinone, phenylhydrazine, hematoxylin, or tertiary butyl catechol, higher temperatures, up toabout 100 C. still temperature, and correspondingly higher vapor pressures not exceeding about 100 mm. of'mercury maybe maintained in the systern without appreciable loss of styrene; in the absence of such inhibitors, higher temperatures lead to increasing polymerization of the styrene.

When carrying out the process of my invenit is dissolved by an azeotropic distillation of the' agent-hydrocarbon solution with water as the charging the agent-hydrocarbon solution to the still with a relatively small proportion of water and subjecting the mixture to fractional distillation. The early distillate consists of azeotropic mixtures of hydrocarbon and water substantially free of agent, or azeotropic mixtures of hydrocarbon, water and relatively small proportions of agent. This distillate is condensed, whereupon it stratifles into two layers. The lower aqueous layer is continuously returned to the column, whereas the upper hydrocarbon layer is returned only in part, to maintain column equilibrium, the remainder being withdrawn. This is continued until nearly all hydrocarbon has been removed from the stillcharge. when such a point has been reached, distillation is continued as before, but the water layer is now withdrawn while the small quantity of'hydrocarbon layer is returned to the still. This is continued until the water has been removed. At this point, the still residue consists of practically pure agent with only a small quantity of hydrocarbon admixed there with. This residue may be reused directly, or it may be subjected to a simple distillation to obtain a colorless product, and this product may then be employed as primary agent in subsequent azeotropic distillations for separation of styrene.

When treating a phenylacetylene containing sary to treat the non-styrene hydrocarbon oil tion in such a way that the oil distillate fractions obtained contain ethylene diamine, i. e. in.

carrying out distillation without the auxiliary agent, water, the distillate fractions are treated to recover the ethylene diamine. The ethylene diamine may be recovered from the hydrocarbon oils in which it is dissolved by extraction with anaqueous solution of a mineral acid. For example; the hydrocarbon solution of agent may-be agitated with a 10% to 30% solution of sulfuric or for removal of agent.

The styrene product may advantageously be subjected to a simple distillation, particularly if it has been withdrawn as still residue rather than final distillate fraction. The styrene may also be agitated with sulfuric acid to remove minute amounts of color bodies, and neutralized with sodium hydroxide prior to said distillation treatment.

The accompanying drawing diagrammatically illustrates the embodiment of the invention involving the separation of styrene and phenylacetylene from a styrene oil containing phenyl: acetylene and involving the use of water as auxiliary agent. It will be understood the invention is not limited to this embodiment and includes the isolation of styrene from styrene oils free of phenylacetylene and with or without the use ofwater as auxiliary agent.

The following example is illustrative of my invention; it" will be understood the invention is not limited to this example. All percentages in the example are by weight, unless otherwise indicated.

Example A styrene concentrate of .carburetted water gasand coal tar originwas employedrnlt was distilling under reduced 7 7 pressure the styrene-containing. oil

'puriiied with of prepared by fractionally its weight or sulfuric acid. 50 36. and separately collecting a narrow fraction having the following characteristics: t

Speciflcgravity at C. i. 0.832 Fractional distillation range V v (5 mm. of mercury) --C..- 13.0-15.5 Styrene, percent by volume ....-percent- 48 Phenylacetylene content ..-do .2

The ratio of hydrocarbon to agent in the azeo-' tropic distillate, initially about 65 to 35, gradually changed to about '75 to 25. Running samples of distillate were examined by extracting them with dilute mineral acid and determinin the refractive indices of the residual hydrocarbon oils as indicative of the styrene content. The styrene content of the hydrocarbon portion of the distillate rose gradually; when it reached 94%, the fractional distillation was discontinued. The still residue was then distilled under a reduced pressure of to mm. of mercury, yielding 40 volume parts of styrene, having a refractive index of 1.545 at 20 C. corresponding to approximately 96% styrene.

yknediamine. and distilling the material from which such tropic mixture has been removed in admixture with ethylene to separate an oil substantially free of phenylacetylene and having a substantially greater styrene content than the original styrene. oil.

4. In a method for increasing the styrene con tent of an oil containing styrene and like boiling aromatic hydrocarbons, including phenylacetylene, the steps which comprise adding ethylene diamine to the oil, and subjecting this mixture to fractionaldistillation to remove an azeotropi'c mixture of the non-styrene aromatic hydrocarbons other than phenylacetylene and ethylene diamine, and leaving as still residue an oil having a substantially greater styrene content than the .7 original styrene oil, and containing substantially By distilling this styrene product in the presence of ethylene diamine, a styrene product containing less than .05% phenylacetylene is obtained as distillate.

Since certain changes may be made in carrying out the above process without departing from the scope-of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

I claim: r

1. In a method for producing a hydrocarbon oil of higher styrene content from an oil containing a lower styrene content and at least one like boiling non-styrene aromatic component, the step which comprises fractionally distilling a mixture of such oil and ethylene diamine to distill of! a substantial portion of said non-styrene aromatic component and produce an oil having a substantially greater styrene content than the original oil.

2. In a method for increasing the styrene content of an oilcontaining styrene and like-boiling aromatic hydrocarbons, the steps which comprise adding ethylene diamine to the oil, subjecting this mixture to fractional distillation to separate an azeotropic mixture of non-styrene aromatic hydrocarbons and ethylene diamine, and recovering from the material from which such azeotropic mixture has been separated an oil having a substantially greater styrene content than the original styrene oil.

3. In a method for increasing the styrene content of an 011 containing styrene and like-boiling aromatic hydrocarbons, including phenylacetylene, the steps which comprise adding ethylene diamine to the oil, subjecting this mixture to fractional distillation to first separate an azeotropic mixture of the non-styrene aromatic hydrocarbons other than phenylacetylene and ethall of the phenylacetylene.

5. In a method for increasing the styrene content of an oil containing styrene and like-boiling aromatic hydrocarbons, the step which comprises fractionally distilling a mixture of such oil and ethylene diamine.

. 6. In a method for increasing the styrene content of an oil containing styrene and like-boiling non-styrene aromatic components, the steps which comprise adding ethylene diamine to the oil in amount suflicient to form azeotropes with at least a part of the non-styrene aromatic components of the oil, subjecting this mixture to fractional distillation to separate as distillate an azeotropic mixture of ethylene diamine and aromatic non-styrene components, and to produce as a second product a material comprising an oil having a greater styrene content than the original oil, and thereafter removing the ethylene diamine from oil fractions in which it is present.

7. In a method for production of substantially pure styrene from an industrial styrene fraction containing like-boiling non-styrene aromatic hydrocarbons, the steps which comprise carrying out continuous fractional distillation of a mixture of such styrene fraction and ethylene d1- amine, said ethylene diamine being present in amount at least sufficient to form azeotropes with the non-styrene aromatic hydrocarbons in the oil vaporized, continuously withdrawing as distillate product an azeotropic mixture consisting predominantly of the ethylene diamine and nonstyrene aromatic hydrocarbons, and continuously withdrawing as residual product a material whose oil component is substantially pure styrene.

8. In a method for increasing the styrene content of an oil containing styrene and like-boiling non-styrene aromatic components, the step which comprises fractionally distilling of a mixture of such oil and ethylene diamine in the presence of a styrene polymerization inhibitor and at a temperature of not more than C.

9. In a method for increasing the styrene content of an oil containing styrene and like-boiling non-styrene aromatic hydrocarbons, the steps which comprise adding ethylene diamine to the oil, subjecting this mixture to fractional distillatillat an azeotropic styrene aromatic hydrocarbons, stratifying the distillate into water and hydrocarbon layers and returning the water to the upper part of the fractionating column, continuing fractional distillation, stratiflcation of distillate, and return of water to the upper part of the column until the greater part of the non-styrene aromatic hydrocarbons has been separated from the styrene oil, and thereafter withdrawing as product a styrene oil richer in styrene than the original oil.

11. In a method for increasing the styrene content of an oil containing styrene and like-boiling non-styrene aromatic hydrocarbons including phenylacetylene, the steps which comprise adding water and ethylene diamine to-the oil, subjecting this mixture to fractional distillation to take oil as distillate an azeotropic mixture of water and non-styrene aromatic hydrocarbons other than phenylacetylene, stratifying the distillate into water and hydrocarbon layers and re-- turning the water to the upper part of the fractionating column, continuing fractional distillation, stratiflcation of the distillate, and return of water to the column until the greater part of the non-styrene aromatic hydrocarbons other than phenylacetylene has been separated from the styrene oil, and thereafter withdrawing as product a styrene oil richer in styrene than the original oil, leaving as still residue an oilcontaining substantially all of the phenylacetylene.

12. In a method for substantially removing phenylacetylene from a styrene oil containing it, the step that comprises fractionally distilling a mixture of such oil and ethylene diamine to drive off as distillate an azeotropic mixture of styrene and ethylene diamine and thereby effect substantially complete separation of phenylacetylene andstyrene.

13. In a method for lowering the phenylacetylene content of the styrene oil containing suflicient phenylacetylene to .aiiect polymerization, the step that comprises fractionally distilling a mixture of such oil and ethylene diamine, to separate as distillate product a styrene oil containing an amount of phenylacetylene insuflicient to affect polymerization.

14. In a method for lowering the phenylacetylene content of a styrene oil containing at least about .05% phenylacetylene, the step that comprises fractionally distilling a mixture of such oil and ethylene diamine, to separate as distillate product a styrene oil containing less than .03% phenylacetylene.

15. A method for increasing the styrene content of an oil containing styrene and like boiling hydrocarbons, including phenylacetylene which mixture of water and nonsubjecting this mixture to fractional distillation to remove an azeotropic mixture consisting predominantly of the ing this mixture to fractional distillation to separate the styrene from the phenylacetylene.

16. In a process of separating styrene from a styrene oil containing components involving the distillation of said oil with ethylene diamine to separate an azeotropic mixture of said like-boiling non-styrene components and ethylene diamine, the step which comprises distilling said mixture in the presence of distillate an azeotropic mix-' ture of said non-styrene components and water water to separate as from the ethylene diamine.

17. In the process of separating styrene from a styrene oil containing like-boiling non-styrene aromatic hydrocarbons involving the ,distillation of said oil with ethylene diamine to separate as distillate an azeotropic mixture of said like-boiling non-styrene aromatic hydrocarbons with ethylene diamine, the step which comprises distilling said mixture in the presence of water to separate an azeotropic mixture of said like-boiling nonstyrene water from the ethylene 18. The process of ethylene diamine and prises distilling said diamine. separating a mixture of hydrocarbons which comwater to distill 01f an azeotropic mixture of said hydrocarbons with water and thus effect the separation of said hydrocarbons from the ethylene diamine.

KARL H. mean REFERENCES ,crrEn The following references are-of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,162,963 McKittrick June 20, 1939 2,308,229 Natta Jan. 12, 1943 2,376,870 Engle May 29, 1945 2,380,019 Bloomer July 10, 1945 2,381,996 Bloomer Aug. 14, 1945 2,385,235 Schneider Sept. 18, 1945 2,398,689 Bloomer Apr. 16, 1946 2,405,300

Greenburg Aug. 6, 1946 l2 r comprises adding ethylene diamine to the oil.

non-styrene hydrocarbons other than phenylacetylene and ethylene di- 2 residue an oil having" and thereafter adding like-boiling non-styrene,

aromatic hydrocarbonsv and mixture in the presence of 

